1. Field of the Invention
This invention relates to semiconductor image sensors having charge-coupled devices (CCD) operating as electro-optic transducers and charge-transfer devices as a self-scanning matrix structure.
2. The Prior Art
There are existing image sensors constructed on the surface of a semiconductor divided into elements arranged horizontal rows and vertical columns. Each element includes a semiconductor photo-sensor and a charge-transfer device connected thereto to connect all of the photo-sensor elements of a vertical column to a vertical shift register. One end of each of the vertical shift registers is connected to the horizontal shift register located on the same semiconductor substrate.
The vertical shift registers are operated in unison to transfer charge carriers from position to position along the vertical shift registers so that they eventually reach the horizontal shift register. The carriers reach the horizontal shift register at the equivalent of one horizontal line of the video image at a time, and they are transferred along the horizontal shift register at a rate equivalent to the horizontal scanning speed of a television system. At the output of the horizontal shift register, the carriers are applied to a utilization circuit.
The conventional elements of an image sensor according to the prior art include an insulating layer on the semiconductor substrate and a transparent electrode on the insulating layer. One part of each element is arranged so that the transparent electrode is spaced from the substrate only by the insulating layer so that photons that reach the transparent electrode can produce minority charge carriers in the region of the substrate directly behind that part of the transparent electrode. The elemental area also includes one electrode of the vertical shift register to which that element is connected. Part of the electrode is separated from the semiconductor substrate by the insulating layer, and between that part and the part of the transparent electrode that is also separated from the substrate only by the insulating layer is a transfer electrode. The transfer electrode is also separated from the semiconductor substrate by the insulating layer, and a part of the shift register electrode overlaps the transfer electrode but is insulated therefrom by additional insulating material. The transparent electrode also extends over the transfer electrode and the shift register electrode but is separated from each of them by more of the insulating material of the insulating layer. An opaque layer overlies the transfer electrode and the shift register electrode, leaving substantially only the area to be illuminated uncoated.
The vertical shift registers of the prior art are operated as two-phase devices, which are clocked at the horizontal repetition rate. The transparent electrode has a fixed voltage applied to it and the transfer electrode is pulsed at field repetition rate so that during one field interval, charge carriers from those elements lying in odd horizontal lines will be transferred to their respective vertical shift registers, and during the remaining alternate field intervals, those elements lying in even horizontal lines will transfer their carriers to their respective vertical shift registers.
The prior art structure requires three types of electrodes, one to receive the proper potential to operate the photo-sensors, another to receive the clock pulses, and a third to transfer charge carriers from the photo-sensor regions to regions controlled by the electrodes operated by the clock pulses.